Process for production of bisphenol A

ABSTRACT

An object of present invention is to provide a process of producing bisphenol A, and more particularly a process of producing bisphenol A having high purity and an excellent hue. 
     In the present invention, in a crystallization step to form the slurry containing adduct crystals,
         (a) a fed solution of bisphenol A in phenol is cooled at the temperatures of at least two steps to form a slurry containing adduct crystals,   (b) at least two crystallization stages having different cooling temperatures are provided, and   (c) when the solid fraction of the slurry is A [% by weight] in the final crystallization stage prior to transporting the slurry into the solid-liquid separation step and the solid fraction of the slurry is B [% by weight] in the crystallization stage in which crystals are first formed, the value of B/A is kept 0.7 or less.

TECHNICAL FIELD

The present invention relates to a process of producing bisphenol A.More particularly, the present invention relates to a process ofproducing bisphenol A having excellent economical efficiency, highpurity and an excellent hue.

BACKGROUND ART

Bisphenol A [2,2′-bis(4-hydroxyphenyl)propane] has been used as astarting material for producing a variety of polymers. In recent years,there has especially been a high demand for aromatic polycarbonateshaving excellent impact resistance and transparency, and bisphenol Ahaving low coloring has been desired for producing aromaticpolycarbonates.

Bisphenol A is usually produced by reacting phenol with acetone in thepresence of homogenous acids or solid acid catalysts. The reactionmixture includes unreacted acetone, unreacted phenol, water producedduring the reaction, and other side-products in addition to bisphenol A.The main component of the side-products is2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl)propane (hereinafter, referred toas “o,p′-BPA”), and in addition, the side-products include trisphenol, apolyphenol compound, a chroman compound, colored impurities and thelike.

Bisphenol A is obtained by cooling the reaction mixture to form a slurrycontaining a crystalline adduct of phenol-bisphenol A (hereinafter,referred to as “adduct crystals”), if necessary, after removingunreacted acetone and water produced during the reaction andconcentrating bisphenol A [a crystallization step], separating theadduct crystals from the slurry [a solid-liquid separation step],washing the separated adduct crystals with phenol, etc. [a washingstep], and then removing phenol by means of distillation or stripping.

As described above, the reaction mixture of bisphenol A contains coloredimpurities. In the steps of producing bisphenol A, the main step ofremoving the colored impurities includes the crystallization step, thesolid-liquid separation step, and the washing step. The purity and thehue of the adduct crystals produced in the crystallization step give aneffect on the purity and the hue of the bisphenol A product. Further,when the adduct crystals produced in the crystallization step are finecrystals, the amount of a mother liquor adhered to the surface ofcrystals per unit weight of crystals is increased. There is alsodeterioration in the separation efficiency of colored impurities in thesolid-liquid separation step and the washing step subsequent thereto.Accordingly, in order to produce bisphenol A, it is important to produceadduct crystals having high purity and good hue and generating a smallamount of fine crystals in a crystallization step.

As a method of producing adduct crystals with high purity and excellenthue, there can be mentioned a method comprising, by using a series ofmulti-stage crystallization tanks, sequentially cooling to the targetedfinal temperature, as described in Japanese Unexamined PatentApplication Publication No. 5-117191, Japanese Unexamined PatentApplication Publication No. 7-258131, and PCT Japanese TranslationPatent Publication No. 2003-528840. However, this method does notdisclose the ratio (=B/A[−]) of a solid fraction B [% by weight] in thefinal crystallization stage to a solid fraction A [% by weight] in thefirst crystallization stage, which is required to obtain adduct crystalshaving high purity as disclosed in the present invention. Further, thismethod is insufficient for producing adduct crystals having high purity,good hue, and a small amount of fine crystals.

Japanese Unexamined Patent Application Publication No. 5-117191discloses a method comprising, by using n-number of crystallizationtowers having an inner cylinder provided with an inlet port at its upperportion, discharging a part of the slurry of adduct crystals in thecrystallization towers, cooling the discharged slurry in a heatexchanger provided at the outside of the crystallization towers, andthen recycling the slurry of adduct crystals into the crystallizationtower, and at the same time at least a part of the slurry of adductcrystals in the n-th stage is heated to dissolve fine crystals and isthen recycled into the crystallization tower. However, since the adductcrystals are easily crushed, the adduct crystals are crushed duringcirculation of the slurry, which inevitably leads to the formation offine crystals. In addition, it is necessary to heat the slurry of adductcrystals having been once cooled, thereby causing energy loss.

Japanese Unexamined Patent Application Publication No. 7-258131discloses a method in which, by using an n-stage cascade ofcrystallization tanks connected in series with the number ofcrystallization reactors n (where n>1), the reaction mixture iscirculated at a circulation rate of at least 500 m³/h in a state wherethe residence time in each crystallization device is set to three hoursor more. In this method, a plurality of crystallization devices whichhas a residence time of at least 3 hours is required, thereby increasingthe cost for their equipment. Further, since a circulation rate of 500m³/hr or more is required, a great amount of power is required.Furthermore, in the case where the circulation of the slurry isperformed at such a large circulation rate, the amount of fine crystalsproduced by crushing the adduct crystals becomes large.

PCT Japanese Translation Patent Publication No. 2003-528840 discloses aprocess of producing adduct crystals using crystallization devices ofone to five stages during a residence time of 2 to 12 hours, by usingone or more crystallization devices having a crystallization tank, acirculating pump and a cooler. In this method, each crystallizationdevice also needs a circulating pump and the adduct crystals are thuscrushed by the circulating pump, thereby forming fine crystals. Inaddition, the hue of bisphenol A obtained by removing phenol from theadduct crystals becomes insufficient.

As such, in the conventional known method comprising sequentiallycooling the reaction mixture to the targeted final crystallizationtemperature by using a series of multi-stage crystallization tanks, theratio (B/A) of a solid fraction B in the final crystallization stage toa solid fraction A in the first crystallization stage which is requiredto obtain adduct crystals having high purity is not disclosed. Inaddition, from the view point of equipment investment, it is known thatthe crystallization devices practically having three or lesscrystallization stages and preferably two crystallization stages arepreferable. In such method, there is a problem that it is difficult toprecisely control the temperature according to a growth process ofcrystals, since the temperature of the slurry in one crystallizationdevice is approximately homogenous. Therefore, it is not possible toprecisely control the temperature according to a growth process ofcrystals.

The present invention relates to a process of producing bisphenol A.More particularly, it is an object of the present invention to provide aprocess of producing bisphenol A having excellent economical efficiency,high purity and an excellent hue.

DISCLOSURE OF THE INVENTION

The present inventors have made extensive and intensive studies forsolving the above-mentioned problems. As a result, it has been foundthat, when a solution of bisphenol A in phenol is cooled at thetemperatures of at least two steps to continuously form adduct crystals,the adduct crystals having high purity and a good hue can be obtained bysetting a ratio (B/A) of a solid fraction B [% by weight] in the finalcrystallization stage to a solid fraction A [% by weight] in the firstcrystallization stage to a specific range. It has also been found thatthe adduct crystals can be continuously and economically obtained bycooling a solution of bisphenol A in phenol using a multi-chamber typecrystallization device having its inside divided into 3 or morecompartments by partitions with at least one of the compartmentsequipped with a cooler. The present invention has thus been completed onthe basis of the findings.

That is, the present invention provides a process of producing bisphenolA comprising:

(1) a step of producing a phenolic solution containing bisphenol A byreacting phenol with acetone,

(2) a crystallization step of cooling the obtained phenolic solutioncontaining bisphenol A in a crystallization device and continuouslyforming a slurry containing adduct crystals comprising phenol andbisphenol A,

(3) a solid-liquid separation step of separating the adduct crystalsfrom the formed slurry, and

(4) a step of producing bisphenol A by removing phenol from theseparated adduct crystals,

wherein, in the crystallization step,

(a) the fed solution of bisphenol A in phenol is cooled at thetemperatures of at least two steps to form a slurry containing adductcrystals,

(b) at least two crystallization stages having different coolingtemperatures are provided, and

(c) when the solid fraction of the slurry is A [% by weight] in thefinal crystallization stage prior to feeding the slurry into saidsolid-liquid separation step and is B [% by weight] in thecrystallization stage in which crystals are first formed, the value ofB/A is kept at 0.7 or less.

Furthermore, the present invention provides a process of producingbisphenol A comprising:

(1) a step of producing a phenolic solution containing bisphenol A byreacting phenol with acetone,

(2) a crystallization step of cooling the obtained phenolic solutioncontaining bisphenol A in a crystallization device and continuouslyforming a slurry containing adduct crystals comprising phenol andbisphenol A,

(3) a solid-liquid separation step of separating the adduct crystalsfrom the formed slurry, and

(4) a step of producing bisphenol A by removing phenol from theseparated adduct crystals,

wherein the crystallization step is performed by using amulti-chamber-type crystallization device having its inside divided into3 or more compartments by partitions with at least one of thecompartments equipped with a cooler, in which the phenolic solutioncontaining bisphenol A is fed into one compartment in thecrystallization device, the produced slurry of adduct crystals issequentially transported into each compartment, and then the temperatureof the slurry in the following stage is controlled to be lower than thatin the previous stage to gradually cool the slurry containing adductcrystals in at least one set of two serial compartments.

BEST MODE FOR CARRYING OUT THE INVENTION

Bisphenol A can be produced by the dehydration condensation reaction ofacetone with an excess amount of phenol in the presence of acidcatalysts. The molar ratio of phenol to acetone is usually in the rangeof 3 to 30, and preferably 5 to 20. The reaction temperature is usuallyin the range of 40 to 120° C., and preferably 50 to 100° C.

Any one of homogeneous acids and solid acids can be used as the acidcatalyst, but are not limited thereto. In view of low corrosiveness ofdevices and easiness in separating the catalyst from the reactionmixture, the solid acid catalyst is preferable.

In a method in which a homogeneous acid is used as a catalyst,hydrochloric acid, sulfuric acid and the like are generally used.Sulfuric acid which can be easily separated is preferably used.

In a method in which a solid acid is used as a catalyst, a sulfonicacid-type cation-exchange resin is generally used. In order to improvethe catalytic activity of a sulfonic acid-type cation-exchange resin, asulfonic acid-type cation-exchange resin and a compound containing athiol group may coexist in the reaction system. As a method of allowinga sulfonic acid-type cation-exchange resin and a compound containing athiol group to coexist, there can be mentioned a method of ionically orcovalently binding a part of the sulfonic acid groups of a sulfonicacid-type cation-exchange resin with a compound containing a thiol group[the way of fixing thiol], and a method of feeding a compound containinga thiol group, which does not form a chemical bond with a sulfonicacid-type cation-exchange resin, together with raw materials into areactor packed with a sulfonic acid-type cation-exchange resin [the wayof adding thiol]. Any one of said methods may be used, but the way offixing thiol which does not need a step of recovering a compoundcontaining a thiol group is preferable. A method of ionically binding athiol compound with a sulfonic acid-type cation-exchange resin is morepreferable. A method of ionically binding a thiol compound with 3 to 40%of a sulfonic acid group is still preferable, and a method of ionicallybinding a thiol compound with 5 to 30% of a sulfonic acid group is evenstill preferable.

The reaction mixture obtained as described above usually includes, inaddition to bisphenol A, unreacted acetone, unreacted phenol, waterproduced during the reaction, and other side-products. The maincomponent of the side-products is2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl)propane, and in addition, itincludes trisphenol, a polyphenol compound, a chroman compound, coloredimpurities and the like. The reaction mixture is separated fromcatalysts. The separated mixture is then cooled in a crystallizationstep, if necessary, after removing unreacted acetone and water producedduring the reaction and a part of phenol, to form a slurry containingadduct crystals.

In the process of producing bisphenol A according to the presentinvention, the solution of bisphenol A in phenol used as a raw materialfor producing adduct crystals is not particularly limited, provided thatthe solution is a mixture obtained by reacting acetone with an excessamount of phenol as described above. However, the concentration ofbisphenol A is 10 to 50% by weight, and preferably 15 to 45% by weight.When the concentration of bisphenol A is less than 10% by weight, therecovery rate of adduct crystals becomes low. When the concentration ofbisphenol A is more than 50% by weight, the viscosity of the slurrybecomes high, so that the transportation of the slurry becomesdifficult. Raw materials for crystallization may include, in addition tophenol and bisphenol A, 5% by weight or less, preferably 3% by weight orless and more preferably 1% by weight or less of water, 3% by weight orless of acetone, and 20% by weight or less, preferably 15% by weight orless and more preferably 10% by weight or less of the side-products,which are produced in the synthetic reaction of bisphenol A. Thetemperature of a solution of bisphenol A in phenol fed into acrystallization step is not particularly limited, provided that thetemperature is higher than temperature Ts [° C.] which causes noprecipitation of adduct crystals. However, in the case where thesolution is fed at higher temperatures than be needed, the heat transferareas of a cooler become large, as well as the energy required forcooling becomes large. Thus, the temperature is preferably in the rangeof Ts to (Ts+40)° C., and more preferably Ts to (Ts+20)° C.

In the crystallization step according to the present invention, asolution of bisphenol A in phenol is continuously fed and is then cooledat the temperatures of at least two steps to form a slurry of adductcrystals. The crystallization step may be performed using acrystallization device in which one vessel is divided into a pluralityof the compartments by means of partitions, or a device in which aplurality of crystallization devices is linked to each other by piping.In addition, the crystallization step is performed so that the value ofB/A may be 0.7 or less when a solid fraction (weight of adductcrystals/weight of the total slurry) of the slurry is A [% by weight] inthe final crystallization stage prior to transporting the slurry from acrystallization step into a solid-liquid separation step and is B [% byweight] in a crystallization stage (a first stage) in which adductcrystals are first formed. When the value of B/A exceeds 0.7, theamounts of impurities in adduct crystals obtained from the finalcrystallization stage become large. Therefore, the hue of the crystalsbecomes bad. In the case where the amount of adduct crystals produced inthe first stage is too small, the efficiency of the device is lowered.Thus, the value of B/A is preferably in the range of 0.03 to 0.05, andmore preferably 0.05 to 0.4. Values A and B are affected by variousfactors such as a temperature of adduct crystals and concentrations ofbisphenol A, water, and impurities in raw materials for crystallization.But, in many cases, these factors except the temperature in the firststage may be generally determined by other processing factors.Accordingly, in order to set the range of B/A value to the above ranges,the value of B is manipulated by appropriately controlling thetemperature of adduct crystals in the first stage to be within the aboverange.

An object of the present invention is to provide also a method in whichthe crystallization step is performed by using a multi-chamber typecrystallization device having its inside divided into 3 or morecompartments by partitions with at least one of the compartmentsequipped with a cooler, in which the phenolic solution containingbisphenol A is fed into one compartment in the crystallization device,the produced slurry of adduct crystals is sequentially transported intoeach compartment, and then the temperature of the slurry in thefollowing stage was controlled to be lower than that in the previousstage to gradually cool the slurry containing adduct crystals in atleast one set of two continuous compartments.

In the multi-chamber type crystallization device, the partitions areprovided with an inlet port. The slurry is transported into acompartment of the next stage through the inlet port. Accordingly, it isunnecessary to use a pump in the transportation of the slurry betweencrystallization tanks, so that adduct crystals are not crushed by atransport pump. Thus, the amount of fine crystals produced is small.Further, it is possible to produce adduct crystals having high purityand an excellent hue using a simple and inexpensive device, as comparedwith the known method using a series of multi-stage crystallizationtanks.

The number of compartments of the multi-chamber type crystallizationdevice is not particularly limited, provided that the number ofcompartments is 3 or more. The number of compartments is preferably 3 to50, and more preferably 7 to 40. When the number of compartments is lessthan 3, the purity and hue of crystals are insufficient. In the casewhere the number of compartments is more than 50, further improvement ofthe purity and the hue is not be expected. The multi-chamber typecrystallization device has at least one cooler. Each compartment is notnecessarily equipped with a cooler. It is however preferable to providea cooler to each compartment since the precise control of the devicetemperature is possible. A slurry of adduct crystals is gradually cooledto a desired temperature using the cooler. The cooled slurry is thendischarged from the multi-chamber type crystallization device.

Each compartment may be equipped with a stirrer for the promotion ofmixing the slurry of adduct crystals. As a cooler, a cooler which usescooling plates capable of flowing a cooling medium is preferable.Partitions, which divide the inside of a crystallization device into aplurality of compartments, may also function as cooling plates. In caseof using partitions as cooling plates, all partitions do not necessarilyfunction as a cooler, and a crystallization device in which a part ofpartitions optionally have a cooling function, may be used. The innerwall of the crystallization device may function as a cooler by thecirculation of a cooling medium in a jacket provided in crystallizationdevice. The jacket may be use in combination with other coolers. Inaddition, it is possible to use a method comprising discharging a partof a slurry from at least one compartment in a crystallization deviceprovided with a cooler in the outside thereof and cooling the dischargedslurry in the cooler and then recycling the cooled slurry to the samecompartment or the compartment of the next stage. However, since theadduct crystals are crushed by a pump, etc. in the case of carrying outthe recycling step, a method using the above partitions as coolingplates or a method using a jacket as a cooler is preferable.

Since adduct crystals having high purity and an excellent hue can beobtained by using the multi-chamber type crystallization device of thepresent invention, as compared with the known method of crystallizing asolution of bisphenol A in phenol using a series of multi-stagecrystallization tanks, it is possible to increase the temperaturedifference between the cooling surface of a cooler and the slurry ofadduct crystals present in the same compartment as the cooling surface,compared with temperature difference in the known process. In addition,one of the features of the present invention is that it is possible toreduce heat transfer areas of a cooler. For example, PCT JapaneseTranslation Patent Publication NO. 2003-528840 discloses that thetemperature difference is preferably in the range of 2 to 6 [K].However, the temperature difference in crystallization devices accordingto the present invention is 15° C. or less, and preferably 10° C. orless. When the temperature difference between a cooling surface of acooler and the slurry of adduct crystals present in the same compartmentas the cooling surface is 15° C. or less, it is possible to produceadduct crystals having high purity, an excellent hue, and a small amountof fine crystals. In addition, it is difficult that adduct crystalsadhere to the cooling surface. Here, in the case where the cooler is acooler which allows a cooling medium to flow therein, the temperature ofthe cooling surface may be considered to be substantially the same asthat of the cooling medium which is flowed in the cooler.

The method of feeding a cooling medium is not limited, provided that thetemperature difference between the cooling surface of a cooler and theslurry of adduct crystals present in the same compartment as the coolingsurface is within the above range. The cooling medium may be separatelyfed into a cooler of each compartment, or the cooling medium may be fedin single operation into one cooler and then the used cooling medium maybe fed into another cooler. The preferable embodiment is a method inwhich at least a part of the cooling medium is used countercurrentlywith respect to the flow of the slurry of adduct crystals. As suchmethod, there can be mentioned, for example, a method comprising:

when feeding the slurry of adduct crystals into the first compartmentand sequentially transporting the produced slurry of adduct crystalsinto each compartment until the slurry reaches the final compartmentwhile gradually cooling, feeding a cooling medium into the coolerprovided in the final compartment and then discharging it therefrom,sequentially transporting the cooling medium into a cooler of eachcompartment in the opposite direction to the flow of the slurry ofadduct crystals, using the transported cooling medium in the cooler ofthe first compartment where the slurry is fed, and finally dischargingthe used cooling medium. In case of performing this method, it is notnecessary to use a device for separately controlling the temperature ofthe cooling medium, and it is economical. The cooling medium is notparticularly limited, but is for example, water, an aqueous ethyleneglycol solution, an aqueous propylene glycol solution, an aqueousphenolic solution or the like can be used.

In the method using a multi-chamber type crystallization device forproducing bisphenol A of the present invention, in the case where it isnecessary to stably perform crystallization operation for a longer term,the places where the cooling surface of a cooler comes into contact witha slurry of adduct crystals may be equipped with a device preventingadduct crystals from adhering to the surface. As a method using a devicewhich prevent adduct crystals from adhering to the surface, there can bementioned a method of forming the flow of slurry on the surface ofcooling plates and a method of providing a device counter-transportingwhile coming into contact with the cooling surface of a cooler, asdisclosed in U.S. Pat. No. 6,090,972 and U.S. Pat. No. 6,100,422,respectively. As the following method, for example, there can bementioned a method wherein cooling plates also functioning as partitionswhich allows a cooling medium to be flowed in are arranged in parallelin a crystallization device and the surface of cooling plates is scrapedby a wiper linked to a shaft, as disclosed in U.S. Pat. No. 6,355,218and U.S. Pat. No. 4,486,395. In addition, a “Cooling Disc Crystallizer”available from GMF GOUDA can be suitably used. In the case of using thedevice counter-transporting while coming into contact with the coolingsurface, the frequency of bringing the cooling surface into contact witha device preventing adduct crystals from adhering to the surface is setto 0.1 to 30 times per minute, and preferably 0.5 to 15 times perminute. When the frequency is less than 0.1 times per minute, the effectof a device preventing adduct crystals from adhering to the surface isinsufficient, while when the frequency is more than 30 times per minute,the power required to scrape the adhered crystals off becomes large.

The multi-chamber type crystallization device can also be suitably usedin the process of producing according to the present invention wherein asolution of bisphenol A in phenol is cooled at the temperatures of atleast two steps to form a slurry containing adduct crystals, the atleast two crystallization stages having different temperatures from eachother are provided, and the value of B/A is 0.7 or less when the solidfraction of the slurry is A [% by weight] in the final crystallizationstage prior to transporting the slurry into a solid-liquid separationstep and is B [% by weight] in the crystallization stage in whichcrystals are first formed. In this case, the multi-chamber typecrystallization device may be used in all of the first stage to thefinal stage, but it is not always necessary to do so. When a solidfraction of the slurry is C [% by weight] in each crystallization stageand compartment, from the first stage to the stage having the value ofC/A of at least 0.3, preferably at least 0.5 and more preferably atleast 0.7, such stages may be performed by the multi-chamber typecrystallization device. By using the multi-chamber type crystallizationdevice from the first stage to the stage having the value of C/A of atleast 0.3, the precise control of a temperature according to a growthprocess of crystals growth becomes easier to obtain adduct crystalshaving excellent purity and an excellent hue. In addition, the formationof fine crystals is prevented. In this case, the value of B is the solidfraction of the compartment, in which crystals are first formed, in themulti-chamber type crystallization tank. The relation between B and C isB<C. The relation between B and C is not particularly limited exceptthat mentioned above. However, when B/C is preferably 0.7 or less andmore preferably 0.5 or less, adduct crystals having higher purity andbetter hue can be obtained.

The temperature difference between the slurries of adduct crystalspresent in two serial crystallization stages or compartments ispreferably 10° C. or less, still preferably 8° C. or less, and evenstill preferably 0.5 to 5° C. When the temperature difference is withinthe above range, the purity and the hue can become better. Inparticular, in an initial crystallization stage or compartment having avalue of C/A of less than 0.4, it is particularly preferable to maintainthe temperature difference 10° C. or less.

On the other hand, as the temperature difference is smaller, the purityand the hue of crystals are improved, but the number of crystallizationstages and compartments however becomes large, so that the processbecomes complex. For more economical performances, while the temperaturedifference in an initial crystallization stage or compartment ismaintained within the above range, two serial crystallization devices orcompartments in which the temperature difference ΔT between the slurriesof a previous crystallization stage or compartment and a followingcrystallization stage or compartment exceeds 10° C. may be present inthe crystallization stage or compartment wherein the value of C/A is 0.4or more, preferably 0.5 or more, and more preferably 0.7 or more. Bythis, it is possible to simplify the crystallization step withoutafflicting severe damage to the purity and the hue of adduct crystals.

In addition, in at least one set of two serial crystallization stages orcompartments, it is necessary that the temperature of the slurry in thefollowing stage is controlled to be lower than that in the previousstage. However, in a part of the crystallization stages or compartments,the temperatures in the previous stage and the following stage may beidentical or the temperature in the following stage may be higher by 5°C. or less than that in the previous stage.

In any method used in the present invention, the total residence time ofthe slurry of adduct crystals is 0.5 to 8 hours, preferably 1 to 4hours, and more preferably 1 to 3 hours. In the case where the residencetime is less than 0.5 hour, the purity and the hue of crystals areinsufficient, while in the case of more than 8 hours, the purity and thehue are also not substantially improved. The temperature of the slurryof adduct crystals in the final compartment is not particularly limited,but is usually 40 to 70° C. The concentration of the slurry of adductcrystals is not particularly limited, provided that the concentration isone capable of transporting the slurry of adduct crystals. Theconcentration of the slurry in the final compartment is usually 10 to60% by weight and preferably 10 to 50% by weight.

The slurry of adduct crystals discharged from the final crystallizationstage is fed into a solid-liquid separation step to be separated intoadduct crystals and a mother liquor. Moreover, the adduct crystals arewashed with phenol, etc. in order to remove a mother-liquor adheredthereto. The adduct crystals obtained by the process of producingaccording to the present invention have high purity and an excellent huein themselves, have a small amount of fine crystals and are obtained aslarge crystals, so that solid-liquid separation and washing are easy.Bisphenol A is recovered by removing phenol from the adduct crystalsobtained from the solid-liquid separation and washing processes. Sincethe adduct crystals have high purity and an excellent hue, bisphenol Aobtained by the process of the present invention has high purity and agood hue and is suitable for raw materials of polymers such as aromaticpolycarbonate.

EXAMPLES

The present invention will be described below with reference to thefollowing examples. In addition, the hue of adduct crystals wasdetermined by thoroughly dissolving 30 g of adduct crystals in 30 ml ofethanol and measuring the absorbance at 420 nm by a spectrophotometerand then converting the measured absorbance into the value of APHA by acalibration curve constructed from the absorbance of an APHA standardsolution. The rate of adduct crystals having a particle size of 100 μmor less was calculated with the amount of crystals passing through asieve having an opening size of 100 μm. The hue of bisphenol A wasdetermined by comparing it with that of the APHA standard solution byvisual inspection.

Example 1

A crystallization device, in which two crystallization tanks equippedwith a stirrer having draft tubes therein were connected in series, wasused. Phenolic solutions containing 35% by weight of bisphenol A and 5%by weight of the side-products of bisphenol A were continuously fed intothe crystallization device at 90° C. so that the residence time in eachcrystallization tank might be one hour. The fed solutions were cooled sothat the temperatures of slurries of adduct crystals in thecrystallization tank in the first stage and the temperatures of thecrystallization tank in the second stage might be 72° C. and 50° C.,respectively. When the device was stabilized, the slurries of adductcrystals in each stage were collected to measure the solid fractions. Asa result, the solid fraction B in the first stage and the solid fractionB in the second stage were 27% by weight and 42% by weight,respectively, and the value of B/A was 0.64. In addition, the rate offine crystals having a particle size of 100 μm or less in thecrystallization tank in the second stage was 18% by weight. The slurryof adduct crystals discharged from the crystallization tank in thesecond stage was centrifuged to recover crystals and the crystals werethen washed with phenol. These adduct crystals had an APHA color of 9.Bisphenol A was obtained by removing phenol from the adduct crystals.The obtained bisphenol A had a good hue with an APHA color of 15.

Example 2

The same procedure was repeated in the same manner as in Example 1except that the temperature of the crystallization tank in the firststage was 76° C. At this time, the value of B was 21% by weight and thevalue of B/A was 0.50. The rate of fine crystals having a particle sizeof 100 μm or less in adduct crystals obtained from the crystallizationtank in the second stage was 15% by weight. The obtained crystals had anAPHA color of 7.

Comparative Example 1

The same procedure was repeated in the same manner as in Example 1except that the temperature of the crystallization tank in the firststage was 63° C. At this time, the value of B was 36% by weight and thevalue of B/A was 0.86. The rate of fine crystals having a particle sizeof 100 μm or less in adduct crystals obtained from the crystallizationtank in the second stage was 27% by weight. The obtained crystals had anAPHA color of 17. The bisphenol A obtained by removing phenol from theadduct crystals had a high value of hue with an APHA color of 35.

Example 3

A crystallization device, in which 5 partitions having an inlet port fortransporting the slurry were introduced in parallel with each other atsame intervals into a horizontal cylindrical-type vessel to divide thevessel into 6 cylindrical compartments having a same volume, eachcompartment being equipped with a jacket capable of flowing water as acooler, was used. In order to stir the inside of each compartment, ashaft was provided on the central axis of the cylindrical vessel and theshaft was then equipped with an agitator blade to stir at 10 rpm. Waterfor cooling the slurry was fed into each jacket. Then, phenolicsolutions containing 35% by weight of bisphenol A and 5% by weight ofthe side-products of bisphenol A were continuously fed at 85° C. into acompartment in the last end of this crystallization device. The producedadduct crystals were sequentially transported into the followingcompartments and then were discharged from the compartment in the lastend (the final compartment) of the other side so that the residence timein a crystallization device might be 2 hours. The temperatures of adductcrystals in each compartment were 81, 77, 72, 66, 58 and 50° C. from theupstream side, respectively. The temperatures of the cooling water inthe inlet of each compartment were 76, 72, 67, 61, 53 and 45° C. fromthe upstream side, respectively. The temperature difference between thecooling surface and the slurry was 5° C. When the device was stabilized,the slurry of adduct crystals was collected to measure the solidfraction. As a result, the solid fraction B in the first compartment was11% by weight, the solid fraction A in the 6-th compartment which wasthe final compartment was 42% by weight and the value of B/A was 0.26.The rate of fine crystals having a particle size of 100 μm or less inthe 6-th compartment was 5% by weight. Moreover, the crystals wererecovered by centrifuging the slurry of adduct crystals discharged fromthe final compartment, and then were washed with phenol. These crystalshad an APHA color of 2. In this state, the operation was continued for100 hours, there was however no change in the hue of crystals and therate of fine crystals having a particle size of 100 μm or less. Theincrease in the slurry temperature in the final compartment which wasobserved in the case where crystals were adhered to a cooling surfacewas also not observed.

Example 4

The same procedure was repeated in the same manner as in Example 1except that, while the temperatures of adduct crystals in eachcompartment were maintained as the same temperatures described inExample 3 which were 81, 77, 72, 66, 58 and 50° C., the temperatures ofcooling water in the inlet of each compartment were set to 69, 65, 60,54, 46 and 38° C. from upstream side of slurry, respectively and thetemperature difference between cooling surfaces and slurries became 12°C. by means of controlling the area of cooling surface in eachcompartment. When the crystallization device was stabilized, theobtained crystals had an APHA color of 5 and the rate of fine crystalshaving a particle size of 100 μm or less was 11 percent. In this state,the operation was continued for 100 hours, and as a result, thetemperature of slurry in the final compartment was 51° C.

Example 5

The same solution of bisphenol A in phenol as in Example 1 was fed at90° C. into the multi-chamber type crystallization device used inExample 3 so that the residence time might be one hour. The temperaturesof the slurry of adduct crystals in each compartment were set to 83, 82,80, 78, 75 and 72° C. from the upstream side, respectively. At thistime, each temperature difference between cooling surfaces and theslurries became 5° C. In addition, the slurry discharged from the finalcompartment was fed into one crystallization tank used in Example 1 toperform crystallization at a slurry temperature of 50° C. during aresidence time of 1 hour. At this time, the solid fraction B in thefirst compartment of the multi-chamber type crystallization device was4% by weight. The solid fraction C in the final compartment was 27% byweight. The solid fraction A in the stirred crystallization tankequipped with draft tubes, which was in the final crystallization stage,was 42% by weight. The values of B/A and C/A were 0.10 and 0.64,respectively. The rate of fine crystals having a particle size of 100 μmor less in the final crystallization stage was 7% by weight. Thecrystals were recovered by centrifuging the slurry of adduct crystalsdischarged from the final crystallization stage and then washed withphenol. These crystals had an APHA color of 3. The multi-chamber typecrystallization device was used until the value of C/A reached 0.3 ormore. As a result, it was found that the hue of adduct crystals wasimproved as compared with that in Example 1 and the rate of finecrystals was decreased. In addition, as compared with Example 3,although the temperature difference ΔT between the slurries of theprevious stage and the following stage was more than 10° C. afterexceeding a value of C/A of 0.4, it was found that there was nosubstantial effect on the hue of adduct crystals and the rate of finecrystals.

Example 6

A crystallization device in which 7 partitions having an inlet port fortransportation of a slurry were introduced in parallel with each otherat same intervals into a horizontal cylindrical-type vessel to dividethe vessel into 8 cylindrical compartments having the same volume, eachcompartment being equipped with a jacket capable of flowing water as acooler, was used. In order to stir the inside of each compartment, ashaft was provided on the central axis of the cylindrical vessel and theshaft was then equipped with an agitator blade to stir at 10 rpm.Crystallization was then performed in the same manner as in Example 3except that the temperatures of adduct crystals in each compartment wereset to 82, 80, 76, 72, 67, 62, 56 and 50° C. from the upstream side,respectively, the temperatures of the cooling water in the inlet of eachcompartment were set to 77, 75, 71, 67, 62, 57, 51 and 45° C. from theupstream side, respectively, and the temperature difference betweencooling surfaces and slurries became 5° C. When the device wasstabilized, the slurry of adduct crystals was collected to measure thesolid fraction. As a result, the solid fraction B in the firstcompartment was 9% by weight, the solid fraction A in the 8-thcompartment which was the final compartment was 42% by weight and thevalue of B/A was 0.21. The rate of fine crystals having a particle sizeof 100 μm or less in the 8-th compartment was 3% by weight. The crystalswere recovered by centrifuging the slurry of adduct crystals dischargedfrom the final compartment and then washed with phenol. The obtainedcrystals had an APHA color of less than 2. In this state, the operationwas continued for 100 hours, there was however no change in the hue ofcrystals and the rate of fine crystals having a particle size of 100 μmor less, and further the increase in the slurry temperature was also notobserved.

Example 7

By means of controlling the flow rate of the cooling water and the areaof cooling surface in each compartment, the temperatures of adductcrystals in each compartment were set to 82, 79, 66, 61, 58, 55, 52 and50° C. from upstream side of the slurry, respectively, and thetemperature difference between the second compartment and the thirdcompartment was 12° C. At this time, the temperatures of the coolingwater in the inlet of each compartment were set to 77, 70, 56, 56, 55,52, 49 and 47° C. from the upstream side of the slurry of adductcrystals, respectively, and the temperature difference between coolingsurfaces and slurries was at most 10° C. Crystallization was thenperformed in the same manner as in Example 3 except the above-mentioneddescription. When the device was stabilized, the slurry of adductcrystals was collected to measure the solid fraction. As a result, thesolid fraction C in the second compartment was 16% by weight, the solidfraction A in the 8-th compartment which was the final compartment was42% by weight and the value of C/A was 0.38. The rate of fine crystalshaving a particle size of 100 μm or less in the 8-th compartment was 13%by weight. The crystals obtained by centrifuging the slurry of adductcrystals discharged from the 8-th compartment had an APHA color of 6.

Reference Example

By using only one of the crystallization devices used in Example 1, thesame solution of bisphenol A in phenol as in Example 1 was continuouslyfed so that the residence time might be 2 hours. The crystallizationtank was then cooled until the inside temperature reached 50° C. Whenthe device was stabilized, the slurry of adduct crystals discharged fromthe lower portion of the crystallization tank was centrifuged to recovercrystals. These crystals had an APHA color of 23. The rate of finecrystals having a particle size of 100 μm or less was 36% by weight.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a processof producing bisphenol A which excels in economical efficiency and hashigh purity and an excellent hue.

1. A process of producing bisphenol A comprising: (A) a step ofproducing a phenolic solution containing bisphenol A by reacting phenolwith acetone, (B) a crystallization step of cooling the obtainedphenolic solution containing bisphenol A in a crystallization device andcontinuously forming a slurry containing adduct crystals comprisingphenol and bisphenol A, (C) a solid-liquid separation step of separatingthe adduct crystals from the slurry, and (D) a step of producingbisphenol A by removing phenol from the adduct crystals, wherein, in thecrystallization step, (a) the fed solution of bisphenol A in phenol iscooled at temperatures of at least two steps to form a slurry containingadduct crystals, (b) at least two crystallization stages havingdifferent cooling temperatures are provided, and (c) when the solidfraction of the slurry is A [% by weight]in the final crystallizationstage prior to transporting the slurry into the solid-liquid separationstep and is B [% by weight] in the crystallization stage in whichcrystals are first formed, the value of B/A is kept at 0.7 or less.
 2. Aprocess of producing bisphenol A comprising: (A) a step of producing aphenolic solution containing bisphenol A by reacting phenol withacetone, (B) a crystallization step of cooling the obtained phenolicsolution containing bisphenol A in a crystallization device andcontinuously forming a slurry containing adduct crystals comprisingphenol and bisphenol A, (C) a solid-liquid separation step of separatingthe adduct crystals from the formed slurry, (D) a step of producingbisphenol A by removing phenol from the separated adduct crystals,wherein the crystallization step is performed by using amulti-chamber-type crystallization device having its inside divided into3 or more compartments by partitions with at least one of thecompartments equipped with a cooler, in which the phenolic solutioncontaining bisphenol A is fed into one compartment in thecrystallization device, the produced slurry of adduct crystals issequentially transported into each compartment, and then the temperatureof the slurry in the following stage is controlled to be lower than thatin the previous stage to gradually cool the slurry containing adductcrystals in at least one set of two serial compartments, and wherein, inthe crystallization step, (a) the fed solution of bisphenol A in phenolis cooled at temperatures of at least two steps to form a slurrycontaining adduct crystals, (b) at least two crystallization stageshaving different cooling temperatures are provided, and (c) when thesolid fraction of the slurry is A (% by weight) in the finalcrystallization stage prior to transporting the slurry into thesolid-liquid separation step and is B (% by weight) in thecrystallization stage in which crystals are first formed, the value ofB/A is kept at 0.7 or less.
 3. The process according to claim 1,comprising feeding the phenolic solution containing bisphenol A into onecompartment of the crystallization device to produce a slurry of adductcrystals, sequentially transporting the produced slurry of adductcrystals to each compartment, and gradually cooling the slurry of adductcrystals, by using a multi-chamber type crystallization device havingits inside divided into 3 or more compartments by partitions with atleast one of the compartments equipped with a cooler is used, until thevalue of C/A is at least 0.3 when the solid fraction in the slurry is A[% by weight]in the final crystallization stage prior to transportingthe slurry into the solid-liquid separation step and the solid fractionin the slurry is C [% by weight ]in each crystallization stage.
 4. Theprocess according to any one of claims 1 to 3, wherein the temperaturedifference between the slurries of adduct crystals present in two serialcrystallization stages or compartments is 10° C. or less.
 5. The processaccording to claim 4, wherein when the solid fraction in the slurry is A[% by weight ]in the final crystallization stage prior to transportingthe slurry from the crystallization step into the solid-liquidseparation step and the solid fraction in the slurry is C [% by weight]in each crystallization stage or compartment, the crystallizationstages or compartments having the value of C/A of 0.4 or more have atleast one set of two serial crystallization stages or compartmentshaving a temperature difference DT between the slurries of the previousstage or compartment and the following stage or compartment of more than10° C.
 6. The process according to any one of claims 1 to 3, wherein ina multi-chamber crystallization device, the temperature differencebetween the cooling surface of a cooler and the slurry of adductcrystals present in the same compartment as the cooling surface is 15°C. or less.
 7. The process according to any one of claims 1 to 3,wherein a device is provided, which prevents adduct crystals ofphenol-bisphenol A from adhering to the cooling surface.
 8. The processaccording to claim 1, wherein, in the crystallization step, the totalresidence time of the slurry of adduct crystals is 1 to 3 hours.
 9. Theprocess according to claim 2, wherein, in the crystallization step, thetotal residence time of the slurry of adduct crystals is 1 to 3 hours.